1. Field of the Invention
The invention relates to an exhaust gas recirculation apparatus of an internal combustion engine and a control method thereof.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-11-229973, for example, describes technology which keeps the temperature of an exhaust gas control catalyst within a predetermined range by having one EGR passage connected downstream of the exhaust gas control catalyst and another EGR passage connected upstream of the exhaust gas control catalyst, and drawing in exhaust gas from the downstream EGR passage when the temperature of the exhaust gas control catalyst is low and drawing in exhaust gas from the upstream EGR passage when the temperature of the exhaust gas control catalyst is high.
Soot and the like tends to adhere to the EGR passages and EGR valves, and a buildup of this soot and the like results in large pressure loss in the EGR passages and changes the flow rate of EGR gas with respect to the opening amounts of the EGR valves. Therefore, at any given opening amount of an EGR valve, the amount of EGR gas recirculated to the intake system ends up being different from what it would otherwise be if no soot were adhered to the EGR passage and EGR valve, which makes it difficult to control the temperature of the exhaust gas control catalyst.
Also, when exhaust gas is drawn in from downstream or upstream of the exhaust gas control catalyst, even if the temperature of the exhaust gas control catalyst is able to be maintained within the predetermined range, the rotation speed of the turbocharger may decrease resulting in slower acceleration of the vehicle.